This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Compute the acoustic scattering for an arbitrary distribution of spheres suspended within a horizontally oriented rectangular phantom. This is accomplished via the multicentered T-Matrix approach, in which spherical expansions and angular spectrum expansions are used to express the scattered fields from the surfaces of the spheres and the surfaces of the phantom, respectively. In order to satisfy the various boundary conditions, transformation matrices are computed to relate spherical expansions to angular spectrum expansions, angular spectrum expansions to spherical expansions, and spherical expansions to translated spherical expansions. The results of numerical examples are computed for some representative cases.